A mass spectrometer (hereinafter, referred to as “MS” (Mass Spectrometer)) is roughly composed of: an “ionization source” for ionizing a sample; an “analyzer” for separating ions according to the ratio of mass/charge, represented by m/ze (wherein m: mass, z: charge number, and e: unit charge); and a “detection and recording part” of ions being separated.
The electrospray ionization technique generally referred to “ESI” (the abbreviation for Electrospray Ionization) is known as one of the methods of ionizing and introducing a sample molecule to an analyzer of MS.
In this electrospray ionization technique, a spray is carried out by applying the high voltage on a sample molecule being brought in ionic state with acid or the like in a solvent.
This electrospray ionization technique is a technique for spraying a sample molecule, which is brought into an ionic state by acid or the like in the solution, by applying high voltage; forming liquid droplets (mist) in micron order, in which many solvent molecules are combined with multi-protonated molecules; and spraying nitrogen to dry and remove the solvent to ionize the sample molecule, followed by subjecting to the above analyzer. As the charge number of ions being generated becomes large in this technique, it may be particularly useful in the measurements of peptide and proteins, respectively.
Here, the electrospray ionization of the sample molecule in the above ionization source of MS is performed by discharging and atomizing (spraying) the sample molecule in small quantities from a column formed of an elongated silica glass generally having an opening with a minute aperture. This column will be referred to as a “microspray column” below.
FIG. 2 is a diagram that simplifies and expresses the configuration of the conventional electrospray ionization technique. The reference numeral 10 denotes a conventional typical microspray column. On the microspray column 10 being formed such that the tip portion thereof has a cusp form, a large number of fillers 10a such as chemical bond type silica gels or the like having a particle size of about 50 μm is formed. In addition, the inner diameter d of the tip portion of the column is about 10 to 15 μm. Furthermore, the outermost tip portion of the microspray column 10 is loaded with a large-sized bead 10b for preventing the discharge of beads, which are also referred to as a flit.
This microspray column 10 is a constituent member of the ionization source of a mass spectrometer 11 and is arranged such that it extends to the front of a pre-column 12 on which a high voltage is loaded. It is configured that fine droplets 14 containing the sample molecule are atomized from the tip portion of the microspray column 10 to the analyzer 13 of the mass spectrometer 11.
However, in the conventional microspray column, the separation efficiency of a chromatograph was insufficient since the particle diameter of the filler in the column was large (generally about 50 μm).
In addition that the particle size of the filler was large, the inner diameter of the tip opening of the above microspray column was also large. Therefore, the discharge amount of the sample increased and the particle size of charged liquid droplets formed by the spray was also large. As a result, in the process in which the solvent was dried and vaporized, the efficiency of transferring charged electrons to the sample molecule in the solvent was not sufficient. In other words, the ionization efficiency of the sample molecule was insufficient.
Furthermore, the microspray column was configured such that many areas without filling with the filler were formed near the tip opening, resulting in a large discharge amount of the sample and a large particle size of the charged droplet formed with the spray.
Therefore, an object of the present invention is to provide a microspray column capable of improving the ionization efficiency, and a high-sensitive mass spectrometer and a mass spectrometric method using this microspray column.